Variation of the mechanical and radiometric properties of LDPE greenhouse films exposed to agrochemicals and solar radiation

Agrochemical substances used in protected cultivation, especially those based on sulphur, iron and chlorine, generate by-products that lead to a degradation of greenhouse plastic films evidenced by the variation of their mechanical and radiometric properties. A research was carried out to evaluate how agrochemicals contamination and solar radiation influence the mechanical and radiometric properties of low density polyethylene (LDPE) films. The LDPE films, manufactured on purpose adding different anti-UV stabilizer systems, were exposed to natural outdoor weathering at the University of Bari (Italy; 41° 05' N) during 2009. Each film was tested as covering of two low tunnels: one was sprayed from inside with commercial agrochemicals containing iron, chlorine and sulphur while the other one was not sprayed and used as control. Mechanical and radiometric tests were carried out on the new films and on film samples taken at the end of the trial. Analyses on absorption of the selected contaminants were carried out in laboratory on the samples taken at the end of the exposure in the field in order to compare the relative effectiveness of the stabilizing systems under evaluation. Additional accelerated aging tests were performed in laboratory on samples taken at the end of the film in-field exposure in order to better differentiate the film tensile properties. The experimental tests showed that at the end of the field exposure the stress at break and the strain at break decreased slightly for the control and sprayed stabilised films while the artificial weathering induced a sharp decrease of their mechanical properties. Radiometric tests showed that the natural weathering together with the agrochemicals did not modify significantly the radiometric properties of the films in the solar and PAR wavelength range. Variations were recorded for the stabilised films in the LWIR wavelength range.